In electro-optical display elements containing liquid-crystal dielectrics, the electro-optical effect of a display can be produced by incorporating pleochroic dyestuffs (the "guest phase") in a liquid-crystal matrix (the "host phase"). In this connection compare the reviews by COX, Mol. Cryst. Liq. Cryst., volume 55, pages 1-32 (1979); JONES and REEVE, ibid., volume 60, pages 99-110 (1980); GRAY, Chimia, volume 34, pages 47-58 (1980) and the literature quoted in these references, all of which are incorporated by reference herein.
However, the dyestuffs used hitherto for this purpose only fulfil inadequately the requirements set for them (for example a high order parameter, satisfactory solubility in the host phase, stability to UV radiation and visible light and stability to voltages up to about 20 V).